Undesired evaporative emission detection routines may be intermittently performed on a vehicle fuel system and emissions control system to confirm that the systems are not degraded. Undesired evaporative emissions detection routines may be performed while the engine is running using engine intake manifold vacuum. However, for hybrid-electric vehicles, engine run time may be limited. As such, undesired evaporative emissions detection routines may be performed when the vehicle is off using engine-off natural vacuum (EONV) generated due to a change in temperature and pressure within the fuel tank following engine shutdown and/or with vacuum supplemented from a vacuum pump. If the systems are sealed from atmosphere, a pressure or vacuum will develop there within responsive to changes in ambient temperature if the systems are intact.
Such routines rely on a functional fuel tank pressure transducer (FTPT) to measure the pressure or vacuum within the fuel system. As such, the rationality of the FTPT must be periodically tested and confirmed. The FTPT may be tested for offset, to determine if a baseline output of the FTPT is accurate. One example approach for an FTPT offset test is shown by Jentz et al. in U.S. Patent Application 2015/0075251. Therein, the fuel tank is vented to atmosphere for a lengthy vehicle-off soak. If the FTPT is functional, a value within a threshold of atmospheric pressure should be output following the vehicle-off soak. A deviation from atmospheric pressure may result in a diagnostic trouble code (DTC) being set at the controller, and/or may result in the FTPT output being adjusted to compensate for any offset.
However, the inventors herein have recognized potential issues with such systems. As one example, venting the fuel tank to atmosphere may result in fuel vapor trafficking to a fuel vapor canister. For vehicles with limited engine run-time, opportunities for purging the fuel vapor canister to engine intake may be limited. This could increase evaporative emissions if a saturated fuel vapor canister is exposed to multiple diurnal cycles. If the engine must be forced on to purge the canister, the fuel efficiency of the vehicle may be reduced.
In another example, U.S. Pat. No. 8,353,273 teaches coupling a fuel tank to a pump in order to generate a pressure signal in the fuel tank and at the position of the pump, and correlating fuel tank pressure with the pressure indicated at the pump. A fault signal may be generated responsive to the correlating.
However, the inventors herein have recognized potential issues with such a system. As one example, coupling the fuel tank to the pump may result in fuel vapors from the tank being routed to the fuel vapor canister, which is undesirable in vehicles with limited engine run-time, as discussed above. Furthermore, the use of an onboard pump adds costs and complexity to the engine system. A diagnostic that does not potentially load the canister and does not include the use of a pump is desirable.
In one example, the issues described above may be addressed by a method for a hybrid-electric vehicle, comprising indicating fuel tank pressure changes from a fuel tank pressure transducer (FTPT) coupled to a fuel tank of a vehicle being diagnosed; receiving fuel tank pressure indications from a select crowd of vehicles; and conducting a rationality test of the FTPT by correlating the indicated fuel tank pressure changes from the vehicle being diagnosed with indicated fuel tank pressure changes from the select crowd of vehicles to diagnose functioning of the FTPT.
As one example, the vehicle being diagnosed sends a request for indicated fuel tank pressure changes comprising a predetermined time period from each of the vehicles comprising the select crowd; wherein the vehicle being diagnosed receives the indicated fuel tank pressure changes wirelessly from each of the vehicles comprising the select crowd; wherein a controller of the vehicle being diagnosed generates an FTPT-based pressure change trend based on the combined data from each of the vehicles that comprise the select crowd; and wherein the generated FTPT-based pressure change trend is further compared to indicated fuel tank pressure changes in the vehicle being diagnosed in order to determine whether the FTPT in the vehicle being diagnosed is functioning as desired. In this way, the FTPT in the vehicle being diagnosed may be diagnosed without coupling the fuel tank of the vehicle being diagnosed to a fuel vapor canister of the vehicle being diagnosed, which may thus reduce undesired emissions.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.